Hereditary non-polyposis colorectal cancer (HNPCC) is an autosomal dominant condition in which affected individuals develop colorectal cancer or extracolonic cancers, most commonly endometrial, at an early age. Recent advances in molecular genetics have led to the identification and sequencing of four genes thought to be responsible for the majority of cases of hereditary non-polyposis colorectal cancer. A description of the disease along with details of the underlying genetics and pathological features are presented. Current management and screening policies in these pedigrees are not clearly established. This article discusses some of the controversies in the light of predictive testing.